Emergency Appeal

In this time of crisis, our front-line staff are working hard to ensure we're still there for the UK's most vulnerable pets. We need your support now more than ever to keep our doors open.

Low energy (lethargy) in dogs

photo of dog on white background


Is your dog sleeping more than usual? Less energetic and less enthusiastic about going for a walk? Slowing down?

If your dog has less energy than normal, we call it lethargy. Lethargy with no obvious cause usually indicates a problem – this can range from something very minor to something much more serious. A full list of all the causes would be very long; this article covers the most common.

Contact your vet if your dog appears ‘under the weather’ or they seem lethargic for no apparent reason.

What is lethargy?

Lethargy means low energy - sleeping more than usual, playing less, being tired and listless. Your dog may even be reluctant to get out of bed, to eat or to greet you.

Sometimes it can be tricky to tell whether your dog is lethargic due to illness, due to age or perhaps just tired after an energetic week. Symptoms often vary and sometimes come and go.

Causes of lethargy

There are very many possible causes of lethargy in dogs, examples include:


Any bacterial or viral infection that causes a fever (high temperature) is likely to make your dog feel very unwell and low on energy.


If your dog is overweight, they will have less energy and find it more difficult to move around. Your vet practice will be happy to help you get them on a weight loss plan and help them to become active again.


Anything that causes pain or discomfort such as arthritis is likely to make your dog feel under the weather and lethargic.

Kidney and Liver Disease

Diseases such as kidney and liver disease can cause sickness and make your dog feel low in energy.


Diseases that cause anaemia (low numbers of red blood cells) are likely to make your dog feel very tired after walks and much less active.

Hormone problems

Untreated diabetes can cause extreme lethargy. This is because your dog is unable to use sugar in the bloodstream for energy. Other diseases like an underactive thyroid cause lethargy.

Heart and lung disease

Heart and lung disease can make it difficult for dogs to exercise.


Some prescribed medicines might make a dog feel lethargic. Speak to your vet if you notice any side effects after giving a prescribed medicine.

Some human medicines can be toxic to pets and many of them will make a dog lethargic if they are eaten accidentally. It’s very important to seek immediate veterinary treatment if your dog has eaten any medication that hasn’t been prescribed for them.


Dogs often eat things they shouldn’t – such as rat poisons. Some human foods such as onions or chocolate can cause stomach upsets and lethargy.

When to contact your vet

If your dog seems low on energy and not quite themselves, get in touch with your vet. Low energy can be caused by many different conditions ranging from very minor problems to more serious – it’s always better to be safe than sorry.

You know your dog best. If you are concerned it’s always best to contact your vet.

Consider insuring your dog as soon as you get them, before any signs of illness start. This will ensure you have all the support you need to care for them.

Published: December 2018

PetWise Pet Health Hub – brought to you thanks to support from players of People’s Postcode Lottery 

Written by vets and vet nurses. This advice is for UK pets only.

Illustrations by Samantha Elmhurst